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Topic: Decompressor woes (Read 1821 times)

In a nutshell, decompressor wont seal so I have no compression.Long story: I was fiddling and dropped the valve into the cylinder, 4 hours later I got it out (at 11pm) so I reassembled the decomp unit, screwed it in by using a socket to push it down while twisting, otherwise I couldn't start the thread.All good I thought, went to start her this morning, no comp and it weezed through the decomp, so Im a little up shit creek without a boat.Do I have to put new washers, more or sealant? I need the bike running asap

Typically, a decomp leak is most often the result of incorrect assembly of the decomp stack. It is very easy to get it wrong, and a lot harder to get it right. I suggest looking at a close-up photo of one which is known to be correct, and compare the assemblies.Most often, this will find the problem, and proper reassembly will cure it.

It is rare that the decomp actually leaks due to a bad seal or a burned seal. If this is the case, then lapping the decomp valve like a regular valve and seat can cure it.However, that is almost never the problem.

You definitely need new washers. Also a good idea to use hi temp silicone around them. When you put it back in use a 13/16 spark plug socket so the valve sticks through the hole and use an open end or box wrench on the socket. ERC

Typically, a decomp leak is most often the result of incorrect assembly of the decomp stack. It is very easy to get it wrong, and a lot harder to get it right. I suggest looking at a close-up photo of one which is known to be correct, and compare the assemblies.Most often, this will find the problem, and proper reassembly will cure it.

Hmm seems I might be missing the main washer, would that cause a bad seal?Otherwise it's properly assembled.

Also is it bad that I could completly remove the valve itself from the head?

If the washer wasn't there, and the decomp wasn't fully seated, that might leak enough to cause issues.And yes, you can remove the whole thing from the head, but you'll need a blanking plug, which was available at one time from Nfield Gear, and it might still be available. If you blank off the decomp, you'll need to use moderate foot pressure to slowly get the leakdown pressure past your rings to get the piston to TDC for kickstarting it. But it can be done like that.

If the washer wasn't there, and the decomp wasn't fully seated, that might leak enough to cause issues.And yes, you can remove the whole thing from the head, but you'll need a blanking plug, which was available at one time from Nfield Gear, and it might still be available. If you blank off the decomp, you'll need to use moderate foot pressure to slowly get the leakdown pressure past your rings to get the piston to TDC for kickstarting it. But it can be done like that.

Ill try some washers then.I meant is it a problem if I can physically remove the valve, shouldnt it be wider that its hole?

Ill try some washers then.I meant is it a problem if I can physically remove the valve, shouldnt it be wider that its hole?

It's the same thread size as the spark plug. Use a spark plug crush washer.If you unscrew the whole thing from its base, it will come right out. Don't pull the cotter pin!If you do take it out and don't have the proper blanking plug, there will be a small hole open there which connects into the exhaust port and you'll have an exhaust leak there. That's where the decomp vents into the exhaust port.

I did take the cotter pin out, this is why I had to do this in the first place Could I use a spark plug with a thread sealer as a temp solution if i cant fix the decomp? Or until a replacemenf can arrive?

I did take the cotter pin out, this is why I had to do this in the first place Could I use a spark plug with a thread sealer as a temp solution if i cant fix the decomp? Or until a replacemenf can arrive?

If you can find a spark plug small enough to fit in there, fine.The boss around the hole usually won't fit a spark plug in there, but you might be able to find a small bodied spark plug.The issue at that point would be the exhaust leak at the dump hole.You could probably plug that temporarily with some silicone sealer. Silicone sealer might fix your decomp leak too, but you have to let it dry for the full 24 hours before you start up the engine. Otherwise it will blow out.

Well this is part of evolving as a human. When I was your age I f'd up something on a daily basis because I had little to no patience. I can't say I don't f up stuff any more, but the frequency is a light years difference from those younger years.

It is definitely a huge bummer because you just bought this bike and had been so excited about owning one for such a long time. The other thing that sucks when you are younger is the observance of time. http://ubiquity.acm.org/article.cfm?id=1455706 Everything seems to move so slow, takes forever to happen. When you get older you wish you could slow everything down a bit. Maybe things have changed as our world shrinks more and more because of technology, but it most likely is or feels the same way.

Learn from this and move on. Hopefully this is not your only transportation, that would really bite.

You should be able to find a local shop to helicoil the head for you. Not to hard of a repair. Everyone here will definitely give you a hand to get you back on the road again. Just remember to take your time and if you run into a problem, think it over or ask for suggestions before you tackle it. You don't want to snowball this thing and create more problems while trying to fix just one.

I feel your pain. I have been on the hook learning how to do all my maintenance myself since the shop here in Austin doesnt sell or service REs anymore. My decomp lever has been stuck and non-operational for a year - I just let the pressure out by hand to hit TDC before I kick her over. I suppose I'll get to fixing it in your honor since you're out of commission. Sucks man. For some reason that thing scares me. haha.

God damn it.Its stripped, the thread is fucked.Looks like the head's gotta come off, sent off, fixed and I'm bikeless for awhile, there goes my good mood for a long time.

Can you see down in the hole with a flashlight? Maybe remove the tank if not. There may be some good threads at the very end of the hole. Take some measurements and source a bolt no longer than the overall depth (or reuse the washers etc to get the required depth) You may be able to just catch the remaining good threads in the head? So long as the bolt doesn't protrude into the chamber. I just did this for an oil line banjo bolt hole that I stripped. Made a new longer banjo bolt to catch the good remaining threads in the hole. May work similar for you. Good luck

Thanks for the help guys, I have no time to do this kinda work before the weekend nor do I trust myself with it after what I did, this is a call in job, lucky there is a few mobile bike mechanics that should be able to fix the thread and make it all work pretty cheap.

this is what I used in place of the OEM decomp thinggie. I bored & tapped a decomp plug I got from Nfeld to fit the decamp button I picked up online. it works great! I put a silicone nipple on the end of the button to keep from burning my phalange!

If the threads are truly stripped out the remaining hole will be just about perfect for the Heli-coil tap. There will be no need for drilling the hole larger.

Some people will insert a long piece of rag down thru the hole to serve as a chip collector After the threads are cut, snagging the rag with a hooked wire and pulling it back out will remove most of the chips.Others will just apply a thick coating of grease to the flutes of the Heli-coil tap before running it into the hole to keep the chips from falling into the cylinder. If this method is used the tap will need to be backed out about every 2-3 turns so the chips can be wiped off and a new layer of grease applied.

In any case, yes, a few chips may find their way into the cylinder but they are aluminum. The bore and piston rings are steel so the aluminum chips won't damage them.About the worst thing that might happen is a chip might get wedged between a valve and it's seat.If this happens, usually the valve will soon cut thru the offending piece and it will be blown out the exhaust along with any other loose aluminum chips.

Most Heli-coils have a driving tang at the bottom to serve to drive the Heli-coil into the threaded hole.This tang needs to be broken off once the insert is in place.Because the tang is steel it could cause a problem if it falls into the cylinder so be very careful at this stage.

If the rag was left in the hole until after the tang is broken off, the tang will probably be caught by the rag and removed when it is pulled out.

I would just take the head off.No big deal. Besides, it's good to take the head off periodically, and it doesn't get so stuck and hard to get off if you do that. If you never take it off, it can be a real bitch when you finally have to do it.

as its got two holes spark plug and decompressor , get the engine at T,D,C on compression take out the spark plug .now you will need a air compressor and the helicoil kit and goggles, put the air in the spark plug hole and tap the thread.this should stop all swarf getting in the engine.BUT WEAR THE GOGGLES

If the head comes off make sure that whoever you are getting to put it on does not over tighten the head nuts. You don't need much more than 20lb/ft, if they get over tightened they can strip out so be careful.

If you came along to the Club meeting next Tuesday chances are some one could help you for free and is likely to know more about these machines than any Jappa mechanic. Of course there is a small annual fee of $35 to join the Club but probably cheaper than RACV. Come along to the meeting anyway, no need to be a member, just to meet a bunch of other Enfield riders, its always a hoot.

Bikes at a good workshop, they'll give a squizz saturday (Public holiday Friday) and I should have her by monday after work.If they need a head gasket at least ill know who they can call, cheers Charles, I should be along Tuesday night.

Like I mentioned before, these inserts are large enough that if a threaded hole was totally stripped out with no old threads at all there would still have enough material left in the hole to produce the Heli-coils oversize threads.

The only thing that might be wrong in using a Heli-coil is one would produce threads from the top of the hole to the bottom and any intersecting side hole would be rather blocked off by the body of the insert.Even this wouldn't be gas tight though. The insert is made by winding a coil of diamond shaped wire into a cylinder and the walls of the cylinder aren't gas tight so some leakage thru the body of the insert to the exhaust would exist.If I were doing it with the head off, after the Heli-coil was installed I would take a grinding stone on my Dremel and grind away the threads that would be blocking the passage to the exhaust port.

Personally, I am not fond of welding up a aluminum casting when the parent material isn't known. Then there is the possibility of the casting being warped due to the welding heat.

You might need to talk to your mechanic a bit more. I would be interested in why a metric Heli-coil wouldn't work.

He's said a Heli coil isnt strong enough and he doesnt trust making a whole thread outta the stuff.The heads off, he will call in the morning and discuss, I want the bike asap as with the payment for this i cant afford petrol for the car, which is falling apart.

Alright I finally conviced him to heli-coil it!He said I wanna get engineers involved to see what we can do rah rahI just said, look Ive had console from guys who race these engines overseas and a helicoil is fine!So Ill have her back today or tomorrow!

MrMazzaJust to add a little support to your decision, when a is Heli-coil installed properly (correct tap used to cut the threads and a dab of thread locking compound on the outside of the Heli-coil to keep it from unscrewing) it will be stronger than the original threaded hole.

Not only will it have real steel threads for the mating part to interface with but the larger external threads on the insert engage a larger area of the aluminum part.To understand this just think of replacing a 1/2-20UNF bolt with a 9/16-18UNF bolt. The larger 9/16 inch bolt will be able to produce or withstand a larger force before it fails.

Hey guys, another update!Thread is all fixed up, just waiting on the new head gasket and decomp valve (The old one was a wee bent so like $5 for a new one) but the old assembly is okay, just the stupid postal service might take until Monday to deliver them.

It's all going well, and my foot/ankle is healing amazingly fast, so I should be riding again by mid next week!